Astronomy & Astrophysics manuscript no. 8329rev c ESO 2021 June 13, 2021 On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope. ⋆ Baldovin-Saavedra, C.1,2, Audard, M.1,2, Carmona, A.1,2 ⋆⋆, G¨udel, M.3, Briggs, K.3, Rebull, L. M.4, Skinner, S. L.5, and Ercolano, B.6,7 1 ISDC Data Centre for Astrophysics, Universit´ede Gen`eve, Chemin d’Ecogia 16, CH-1290 Versoix, Switzerland 2 Observatoire Astronomique de l’Universit´ede Gen`eve, Chemin de Maillettes 51, CH-1290 Sauverny, Switzerland 3 University of Vienna, Department of Astrophysics, T¨urkenschanzstrasse 17, A-1180 Vienna, Austria 4 Spitzer Science Center, California Institute of Technology, 220-6 1200 East California Boulevard, Pasadena, CA 91125 USA 5 Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA 6 Universit¨ats-Sternwarte M¨unchen, Scheinerstrasse 1, 81679 M¨unchen, Germany 7 Cluster of Excellence Origin and Structure of the Universe, Boltzmannstrasse 2, 85748 Garching, Germany Received XX; accepted XX ABSTRACT Context. The [Ne II] line 12.81 µm was proposed to be a good tracer of gas in the environments of proto-planetary disks; its origin is explained by different mechanisms: jets in outflows, photo-evaporative disk winds driven by stellar X-rays/EUV or by the X- ray irradiated proto-planetary disk atmosphere. Previous Spitzer studies gave hints toward the neon emitting mechanism by exploring correlations between the line luminosity and properties of the star-disk system. These studies concluded that the origin of the emission is likely related to accretion and outflows, with some influence from X-rays. Aims. We provide direct constraints on the origin of the [Ne II] emission using high-spatial and spectral resolution observations that allow us to study the kinematics of the emitting gas. In addition we compare the [Ne II] line with optical forbidden lines. Methods. We obtained high-resolution ground-based observations with VISIR-VLT for 15 stars and UVES-VLT for three of them. The stars were chosen for having bright neon emission lines detected with Spitzer/IRS. The velocity shifts and profiles are used to disentangle the different emitting mechanisms producing the [Ne II] line. A comparison between results from this study and previous high-resolution studies is also presented. Results. The [Ne II] line was detected in 7 stars, among them the first confirmed detection of [Ne II] in a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate an origin in a jet. In two stars, the small shifts and asymmetric profiles indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to edge-on, shows a spatially unresolved line centered at the stellar rest velocity, although cross-dispersion centroids move within 10 AU from one side of the star to the other as a function of wavelength. The line profile is symmetric with wings extending up to ∼±80 km s−1. The origin of the [Ne II] line is unclear and could either be due to the bipolar jet or to the disk. For the stars with VLT-UVES observations, in several cases, the optical forbidden line profiles and shifts are very similar to the profile of the [Ne II] line, suggesting that the lines are emitted in the same region. A general trend observed with VISIR is a lower line flux when compared with the fluxes obtained with Spitzer. We found no correlation between the line full-width at half maximum and the line peak velocity. The [Ne II] line remains undetected in a large part of the sample, an indication that the emission detected with Spitzer in those stars is likely extended. Key words. ISM: jets and outflows – Infrared: stars – Protoplanetary disks – Stars: formation – Stars: pre-main sequence 1. Introduction with a planetary system, we need to better understand the disk itself: its composition, size, dynamics, timescales. Protoplanetary disks are the outcome of the star formation process. They provide the material for the young star and arXiv:1205.2182v2 [astro-ph.SR] 23 May 2012 its planetary system. The central star indeed accretes mat- The Spitzer Space Telescope (Werner et al. 2004) made ter from the disk until reaching its final mass, after . a large contribution to the studies of protoplanetary disks 10 Myr (e.g., Mannings & Sargent 1997; Haisch et al. 2001; in the mid-infrared (mid-IR) by revealing the presence of Hillenbrand 2008; Fedele et al. 2010). In order to construct a de- many emission lines from organic molecules (Carr & Najita tailed picture of the process that turns a pre-main-sequence star 2008), water (Carr&Najita 2008; Salyketal. 2008; surrounded by an optically thick disk into a main-sequence star Pontoppidanet al. 2010), and atomic species (Pascucci et al. 2007; Lahuis et al. 2007; Flaccomio et al. 2009; G¨udel et al. 2010; Baldovin-Saavedra et al. 2011). Among the many emis- ⋆ Based on observations made with ESO Telescopes Kueyen/UT2 sion lines detected by Spitzer, [Ne II] 12.81 µm gained particular and Melipal/UT3 at the Paranal Observatory under programmes ID interest. It was proposed to be a good diagnostic of gas in the 083.C-0471, 084.C-1062, 086.C-0911, and 286.C-5038 upper layer of the disk, and is used to study the interaction ⋆⋆ Now at the CRNS-INSU/UJF-Grenoble 1, Institut de Plan´etologie between stellar high-energy irradiation and the disk. Currently et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F- there are three main mechanisms that could explain the presence 38041, France of [Ne II] in the environment of young stars: 1 Baldovin-Saavedra et al.: On the origin of [Ne II] emission in young stars: VLT observations – Irradiated disk atmospheres (Glassgold et al. 2007). In this servations. The stars in our sample are mainly optically thick scenario, the X-rays from the central star create a warm at- disks (Class II). We included a Class I object ( L1551 IRS mosphere composed of gas in atomic form on top of a cooler 5) that has a bright [Ne II] line detected in the Spitzer spec- molecular layer. [Ne II] would be emitted in a region within trum, and an intermediate-mass Herbig Be star ( V892 Tau) be- 20 AU from the central star, the giant planet formation re- cause its low resolution spectrum hinted toward neon emission, gion. but just below the detection threshold (Baldovin-Saavedra et al. – Photoevaporative disk winds driven by EUV (Clarke et al. 2011). The stars known to be jet-driving sources are: CoKu Tau 2001; Alexander et al. 2006), X-rays (Ercolano et al. 2009; 1 (Eisl¨offel & Mundt 1998), XZ Tau (Krist et al. 2008), L1551 Owen et al. 2010) or FUV (Gorti et al. 2009). IRS 5 (Rodr´ıguez et al. 2003), and UY Aur (Hirth et al. 1997). – Shocks (Hollenbach & McKee 1989; Hollenbach & Gorti To our knowledge, the rest of the stars do not have reported out- 2009) and jets (Shang et al. 2010). High velocity outflows flows or jets in the literature. In addition, among the targets se- from the star interacting with the surrounding material lected the following are binaries not resolved by Spitzer: MHO-1 can create strong shocks heating gas to high temperatures. and MHO-2 (3′′. 9 separation, Kraus & Hillenbrand 2009), V892 [Ne II] would be a good tracer of material at velocities Tau (0′′. 05, Smith et al. 2005; Monnier et al. 2008), FS Tau A higher than 40-50 km s−1. (0′′. 24, Hartigan & Kenyon 2003; Hioki et al. 2011), UY Aur (0′′. 88, McCabe et al. 2006), XZ Tau (0′′. 30, Haas et al. 1990), Given the modest spectral resolution of the Spitzer infrared V853 Oph (0′′. 3, McCabe et al. 2006), and CoKu Tau 1 (0′′. 24, spectrograph (IRS; R ∼ 600, i.e., a velocity resolution of ∼ Padgett et al. 1999). Table 1 summarizes the stellar properties of 500 km s−1; Houcketal. 2004) the lines detected are unre- the stars selected for this high-resolution spectroscopy follow- solved. Ground-based observations at high spectral resolution up. are needed in order to determine the origin of the neon-emitting The scope of this study is to obtain high-resolution spectra mechanism, but the number of high-resolution spectra is still of the [Ne II] line (12.81355 µm, Yamada et al. 1985), and by small. Herczeg et al. (2007) detected the [Ne II] emission line determining the line center and studying the profiles, to obtain in one out of three spectra of young circumstellar disks ob- observational constraints on the emission mechanism of [Ne II]. served with the mid-infrared spectrograph on Gemini North The article is organized as follows: in Sect. 2.1 we describe the (R ∼ 30000). Based on the measured linewidth they ruled out VISIR observation strategy and data reduction, in Sect. 2.2 we an accretion flow origin, favoring the photoevaporative theory. present complementary observations obtained in the optical with van Boekel et al. (2009) presented high resolution ground-based UVES-VLT and its data reduction, in Sect. 3 we present the re- spectroscopy (VISIR-VLT) of the young T Tau triplet, succeed- sults, the discussion in Sect. 4, and finally the conclusions in ing in spatially separating the N-S components. These observa- Sect. 5. tions showed that the [Ne II] emission is strongly dominated by outflows heated by shocks. Pascucci & Sterzik (2009) ob- served 6 targets with VISIR-VLT. For 3 stars in the sample, the 2. Observations & Data Reduction line is spectrally resolved, and the line profiles are consistent 2.1.